The present invention relates generally to processing and displaying digital documents and, more particularly, to the conversion of alpha-multiplied color data in a graphical processing system.
In graphical processing, an image can be represented as a rectangular array of sample values. Each sample value represents a color and may include a number of elements referred to as colorants. For example, an image sample in RGB color space includes three colorant values: one for each red, green, and blue. Likewise, an image sample in CMYK color space may include four colorant values: one for each cyan, magenta, yellow, and key (black). An image may approximate the appearance of some natural scene (e.g., a digitized photograph) or may be synthetically generated through any convenient graphics program such as PHOTOSHOP by Adobe Systems Incorporated of San Jose, Calif.
The transparency of a graphical object indicates the extent to which an underlying object may be seen through it. In graphical processing, an object's transparency is implemented through a technique known as blending. Blending generally involves combining a foreground color, associated with a foreground graphical object, and a background color, associated with a background graphical object, to create a third color. Blending can give an object the appearance of being translucent.
Another way to describe an object's transparency is to specify its opacity. Opacity refers to the degree of an object's opaqueness and is also known as "alpha" (.alpha.). An opaque object always obscures any object already printed (or rendered) at the same location, and thus always appears in front of (overlies) previously printed (rendered) objects.